Because of the increased costs of liquid fuels, such as gasoline and diesel fuel, as the energy source for engines in automobiles, trucks, buses, boats, ships, aircraft, tractors and off-the-road construction equipment such as cranes, earth movers and bulldozers, all of which are considered to be vehicles for the purpose of this invention, there has been increased interest in using natural gas to fuel such engines. Also, in many areas of the world natural gas is abundantly available while petroleum products such as gasoline and diesel fuel are very scarce and expensive. Additionally, natural gas fueled engines generally produce combustion products which have a much lower polluting effect than do gasoline and diesel fuel.
Because natural gas at ambient temperature and atmospheric pressure has a relatively low volumetric energy content it is not practical to store it at these conditions in a vehicle fuel tank. Therefore, it is customary to store the natural gas in a fuel tank under very high pressures of about 2000 to 4000 psig. See Swenson et al U.S. Pat. No. 5,107,906; Pierson U.S. Pat. No. 4,987,932; Fisher et al U.S. Pat. No. 4,527,600 and Young U.S. Pat. No. 4,505,249.
It has been previously proposed to store a cryogenic liquid fuel, such as liquefied natural gas, in an insulated fuel tank at a saturated thermodynamic state wherein the liquid is in equilibrium with the vapor. Mills U.S. Pat. No. 4,406,129 discloses a cryogenic liquid fuel in a vehicle tank and the use of the liquid and vapor to fuel a vehicle engine. However, this patent does not disclose the source of the cryogenic liquid fuel, how it was dispensed or filled into the vehicle tank or its temperature and pressure in the tank.
It has been recognized for many years that a very practical way to store bulk quantities of liquefied gases in a tank is at low pressures and low temperatures. For example, liquefied natural gas may be stored at a pressure of about 15 psig to 45 psig and a temperature of about -242.degree. F. to -222.degree. F. See Maher et al U.S. Pat. No. 3,195,316. Storing liquefied natural gas at such a low pressure in a vehicle tank, however, may be undesirable because the low pressure may be unsuitable for practical operation of some engines, particularly fuel injected engines. A need accordingly exists for improved apparatus and methods of filling a vehicle fuel tank with liquefied natural gas.